4.5 inch stroke question

hiiv got a standard bore 400 im looking to recoiv been looking into stroker kits and for not much more *** u can get a 4.5 inch stroke crank rather then a 4.21 or 4.25.is the stroke to rod ratio to much(6.8 inch rods i think)is the standard block ok for this much stroke?is any clearancing of the block required?im after a mild street engine with lots of low end torqueheads will be mildly ported cast iron for now, perhaps edelbrock laterblock is 2 bolt mains with studsi want a reliable street engine, m i good to go with this set up or am i better off sticking to a smaller stroke?thanks

6.8" rod is used in the kits. You will need to install 4 bolt main caps. Caps are not expensive, but the machine work is and will cost you $1000 total. This is a must as the side load on the caps is very high with the long stroke.

Pontiac engineers were very smart matching ratios and head flows. Just think a 4.25" stroke is the same as a Chevy 540. The 455 is a torque monster with 4.21". The 455 has a great rod:stroke and bore:stroke ratios. However, going to a 4.5", the bore:stroke ratio is not so good so they work much better with a .250 larger piston in an aftermarket block. Addition, this will be a lot of cubic inches for the heads. Heavily ported iron heads, and mildly ported E heads do not have the efficiency to maintain torque and also flow at RPM. The long stroke really needs at least a 320cfm head to work well.

For a decade I watched Chevy guys keep adding cubic inches with longer and longer strokes, yet the cars do not go any faster. A guy would increase stroke 3 times over a few years, but no gains because they had the same heads, intake, cam, etc... You are just trading hp to gain torque until you invest in the heads and total combination.

I have built dozens of Pontiac's and my advise is the 4.25" stroke is plenty to make combos such as 500hp 580ft lbs, 600hp and 630ft lbs, and even 700hp. I do have 4.5" stroke now in my car, but I have 535 cubic inches with 370cfm heads 830hp on pump gas. I could have gone 4.75" or 5", but I would not have made any more power, and had a less efficient engine.

Well said Ryan! That was definitely the case when many guys started building 383 small blocks (I realize you are talking about BBC's, but the idea is the same)and then cheaped out on heads. They would realize that they needed large chamber heads to keep the CR down, so they bolted on a set of smogger heads and wondered why the guy with a 350 and decent heads just went by them! For a low(er) buck view on this topic, check out the post "Another 400 rebuild question" where we've covered the low buck alternative for cars that are more cruiser/street oriented where goals of 12's or slower are the plan.Steve
A little help... 'cause we don't all have to learn the hard way!